1. Field of the Invention
The present invention relates to a light-emitting semiconductor device that emits blue light and uses a nitrogen-Group III compound.
2. Description of the Prior Art
It has been known that a GaN compound semiconductor may be used to obtain a light-emitting diode (LED) which emits blue light. This semiconductor device is useful because of its high luminous efficiency resulting from direct electron transition and because of its ability to emit blue light, which is one of the three primary colors.
Recently, it has been found that doping Mg as an impurity and irradiating electrons into a GaN layer can change it into a GaN layer of p-type. As a result, the use of a GaN light-emitting diode with a PN junction instead of a junction of an N-layer and a semi-insulating I-layer is being suggested
There exists, however, a problem of wavelength with the above device. The wavelength of light from such an LED with a PN junction is about 430 nm, or shorter than that of blue light.